1. Field of the Invention
This invention relates to a web winder for winding up web on a core and a method of and a system for automatically wrapping the leading end portion of the web around the core in the web winder.
2. Description of the Prior Art
When tuck is formed in the leading end portion of a rolled strip of paper, metal foil, fabrics or the like, the tucked portion can adversely affect equipment for handling the rolled strip, or the tucked portion must be wasted in the case where the tucked portion is unsuitable for use. Accordingly, in an web winder which slits wide web in a continuous length into a plurality of strips in a continuous length and winds up each strip on a core, there have been used a method of and a system for automatically wrapping the leading end portion of the strip around the core so that tuck is not formed in winding of the trailing portion of the web.
An example of such a system is disclosed in Japanese Unexamined Patent Publication No. 62(1987)-83963. The apparatus will be described with reference to FIG. 16, hereinbelow.
In FIG. 16, reference numerals 201 and 202 denote surface drums, reference numeral 204 denotes a rider roller and reference numeral 203 denotes a core. The core 203 is supported on the surface drums 201 and 202 and is driven by the drums 201 and 202 to wind thereon web 209. The web 209 is cut by a cutter 253 on a table 251 and then the leading end portion is folded along the core 203 by an air blower 252 prior to initiation of winding. Thereafter, a roller device 260 having a pair of small diameter rollers 259 moves toward the core 203 and presses the web 209 against the core 203. The roller device 260 is shown in FIG. 17.
If winding is initiated when the leading end portion is of excess length, the excess length portion forms tuck. In order to avoid formation of tuck, the web 209 is reversed by a length corresponding to the excess length by moving an adjustment roller 254 in the direction of the arrow in FIG. 16 and reversing the surface drums 201 and 202 so that the leading end of the web 209 stops immediately before a "roll-in position" in which the trailing portion of the web 209 begins to overlap the leading end portion.
The length by which the web 209 is reversed is measured by one of sensors S1, S2 and S3 which are disposed according to the diameter of the core 203 used. The roller device 260 brings the leading end portion of the web 209 into close contact with the surface of the core 203 so that the trailing end portion of the web 209 can overlap the leading end portion without formation of tuck when winding operation is initiated. When the surface drums 201 and 202 rotates in the regular direction in the winding operation and the leading end of the web 209 passes the roll-in position, the roller device 260 returns to the original position and the rider roller 204 is brought into contact with the web 209 to press the web 209 against the core 203. Thus the web 209 is wound on the core 203 with the core 203 held by the surface drums 201 and 202 and the rider roller 204.
In order to successfully wind the trailing portion on the leading end portion without formation of tuck, one of the small diameter rollers 259 nearer to the roll-in position than the other should be as near to the roll-in position as possible. For this purpose, the diameter of the nearer small diameter roller is as small as possible. At the same time, link mechanisms 261 and 262 for moving the small diameter rollers 259 are arranged to move the rollers 259 toward the core 203 while adjusting the orientation of the rollers according to the diameter of the core 203.
However the conventional system for automatically wrapping the leading end portion of the strip around the core is disadvantageous in that it takes a long time to reverse the surface drums 201 and 202 and to move the adjustment roller 205 in order to reverse the web 209.
The time required to reverse the web 209 adds to the total time required to produce a rolled web and decreases the productivity of the rolled web. This problem is especially serious when the lot size is small and the number of turns of each roll is small.
Further, the small diameter roller for wrapping the leading end of the web is apt to be deflected because it has a small diameter and a low rigidity, and accordingly the leading end portion of the web cannot be pressed against the core under uniform pressure. When the pressure fluctuates in the direction of width of the web, the leading end portion cannot be uniformly fed to the roll-in position, which can result in wrinkle and/or slack in the leading end portion of the rolled web obtained, and can cause a part of the side edge of the rolled web to project in the axial direction of the roll.
Further, in a conventional surface winder, a core is held by a pair of long surface drums and a single rider roller which is substantially equal to the drums in length and is rotated by the drums with a plurality of web strips obtained by slitting wide web nipped between the drums and the rider roller, whereby the strips are wound up on the core.
Generally, the thickness of the web fluctuates in the direction of width of the web. For example, the thickness of the web can fluctuate by several .mu.m per 100 mm in the direction of width. When such web is slitted into strips and the strips are wound up at one time by the winder, the roll diameter differs from strip to strip due to the difference in thickness.
The difference in the roll diameter causes difference in pressure imparted to the strips by the surface drums and the rider roller, which causes the winding tightness to differ from strip to strip. When the winding tightness is excessive, the strip can be wrinkled and, in the case where the web is sensitized paper, the quality of the paper can be diminished. When the winding tightness is poor, the rolled strip can slack.
Further the difference in the roll diameter causes difference in surface speed, which can cause slip between part of the strips and the rider roller, and can result in scratch on the strips.